The invention relates to tripod joints. The joints include an outer joint part, with three uniformly circumferentially distributed axis-parallel recesses forming circumferentially opposed tracks, and an inner joint part, with a tripod shaped cross-section and three circumferentially distributed arms which extend into the recesses of the outer joint part. Roller assemblies are supported on the arms. Each roller assembly includes at least one inner ring and one outer roller. The roller surface of the outer roller rolls directly on the track, with surfaces in each case being paired, such surface pairing enabling at least one radial sliding movement of at least part of a roller assembly relative to the associated arm.
Tripod joints are known which include a number of different designs, examples being DE-PS 27 48 044, DE-PS 28 31 044 and Application 39 36 601.4. In each case, it is the object of the roller assembly selected that the friction forces leading to vibration excitations from the articulated joint when the rollers move relative to the outer joint part should be reduced by changing to a pure rolling movement, with only the radial sliding movement of the roller assembly relatively to the arm and the angular movement of the roller assembly relative to the arm being accommodated by friction bearings subjected to higher friction loads.
There exists a problem of the above designs in that the sliding movements, especially if they affect parts in line contact, such as a ball head located in a cylindrical sleeve, require lubricants suitable for being subjected to very high loads. This considerably increases the costs of the lubricants and thus of the joint as a whole.
It is the object of the present invention to provide an efficient joint which reduces the cost of the required lubricant. The objective is achieved by providing a space encapsulated relative to the remaining joint interior for storing a first lubricant for the surface pairs permitting the radial sliding movement. The remaining joint interior is filled with a second lubricant. The means enables the volume of the high-grade greases used for lubricating the sliding movements of parts to be considerably reduced. The very much larger remaining joint interior is filled with a standard grade grease at considerably reduced costs. The latter is subjected to substantially only rolling surface loads, these loads being the rolling movement of the outer roller on the tracks in the outer joint part and possibly the rolling movement in a roller bearing in the roller assembly.
As with an articulated joint, the radial movement component of the arms relative to the outer rollers leads to changes in the geometric conditions between the slidingly movable and pivotable parts. Preferably a resilient element is used to contain the lubricant volume and enable the volume to be adjusted without losing any lubricant or without exchange of the encapsulated first lubricant and the second lubricant in the remaining joint interior. If the arm is directly radially movable in a roller carrier or inner ring, the resilient element may be provided, especially in the form of a resilient cover, to seal the cross-section of the arm radially outside its surface. In addition, it is possible to use a resilient collar which encloses the arm neck below the roller assembly and forms a supplementary space containing an encapsulated volume of lubricant. However, it is also possible to do without the latter if the lubricant is contained between the arm and the cover.
From the following detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.